1. Field of the Invention
The present invention relates to a cellular phone, and more particularly, to a cellular phone with an insulating envelope for preventing leakage of electromagnetic radiation.
2. Description of the Prior Art
A cellular phone comprises a housing, a circuit board installed inside the housing, and an antenna installed at a top end of the housing. The many different functional units on the circuit board can be roughly classified into three parts based on their functions. These three parts are: a first RF circuit, a second RF circuit, and a base band circuit. The main components of the first RF circuit include an antenna connector, a duplexer, and a power amplifier. The second RF circuit comprises an RF transmitter circuit and an RF receiver circuit. When the cellular phone is transmitting RF signals, the power of the transmitted RF signals is strong and may influence, or even interfere with, other functional units. This noise interferes with many functional units such as the RF receiver circuit, the RF transmitter circuit, and the baseband circuit. Interference with the RF receiver circuit causes reduced sensitivity to received signals, which is undesirable for a cellular phone. A device is necessary to properly insulate the functional units from such radiation interference so that the sensitivity of the cellular phone to incoming signals can be improved and the cellular phone can operate normally.
Shielding the functional units of the cellular phone from radiation interference and improving the sensitivity of the cellular phone is often accomplished by electrically grounded metallic shields installed on the circuit board of the cellular phone. Also, a thin metallic layer is often coated on the inner side of the housing for preventing electromagnetic radiation in the interior of the cellular phone from leaking out. This reduces radiation leakage and prevents electromagnetic interference from occurring. Thus, the metallic shields and the metallic layer on the inner side of the casing can reduce the radiation interference for the functional units, improve the sensitivity of the cellular phone to incoming signals, and reduce the radiation that escapes from the cellular phone.
Please refer to FIG. 1 to FIG. 3. FIG. 1 is a schematic diagram of a cellular phone 10 according to the prior art. FIG. 2 is a side view of the cellular phone 10 shown in FIG. 1. FIG. 3 is an exploded diagram of the cellular phone 10 shown in FIG. 1. The cellular phone comprises a front casing 12, a rear casing 14, a circuit board 20 installed between the front casing 12 and the rear casing 14, an antenna 16 installed at the top end of the rear casing 14, and a battery 18. The rear casing 14 and the circuit board 20 individually comprise four screw holes 15 (shown in FIG. 4) for fixing the rear casing 14 via the circuit board 20 to the front lid 12.
Please refer to FIG. 4. FIG. 4 is a schematic diagram of the circuit board 20 as seen from the direction labeled as xe2x80x9cAxe2x80x9d in FIG. 3. The functional units of the circuit board 20 include an antenna connector 22 electrically connected to the lower end of the antenna 16, a duplexer 24 for separating the emitted RF signals and received RF signals, a power amplifier 26 used for amplifying the power of the emitted signals, an RF receiver circuit 28 for receiving RF signals and converting them into baseband signals, an RF transmitter circuit 30 for processing the baseband signals from the baseband circuit 32 and converting them into RF signals, and a baseband circuit 32. As shown in FIG. 4, the power amplifier 26 with the duplexer 24, the RF receiver circuit 28, the RF transmitter circuit 30, and the baseband circuit 32 on the circuit board are respectively covered by grounded metallic shields 34, 36, 35, 37 to prevent electromagnetic interference.
The power of the transmitted RF signals is strong, so RF noise may be emitted from the power amplifier 26, the duplexer 24, and the antenna connector 22. Since the RF noise comes from more than one source, it is preferred in the conventional art to shield each possible noise source to ensure that each functional unit functions well. The metallic shields 34, 35, 36, 37 diminish radiation interference for these functional units and maintain the sensitivity of the cellular phone 10 to incoming signals. However, these metallic shields 34, 35, 36, 37 increase the cost and the weight of the cellular phone 10.
To reduce the radiation that leaks outside of the cellular phone, and to minimize interference caused by external radiation entering the cellular phone, the inner sides of the front casing 12 and the rear casing 14 of the cellular phone 10 are coated with a thin metallic layer of low impedance. When the rear casing 14 is screwed to the front casing 12, the metallic layer on the inner side of the rear casing 14 electrically connects with the electric ground layer of the circuit board 20. This improves grounding and prevents RF signals in the interior of the cellular phone from leaking out of the cellular phone, and also prevents radiation from outside of the cellular phone from interfering with the interior circuits of the cellular phone.
RF signals in close proximity to the antenna connector 22 are strong and an induced current is therefore easily generated in the metallic layer on the inner side of the rear casing 14 by the RF signals in the interior of the cellular phone. Because the coated metallic layer on the inner side of the rear casing 14 is grounded only via screws, the grounded area is not very large. Therefore, the grounding is poor and any induced current will emit more radiation that further interferes with each of the functional units within the cellular phone.
If many metallic shields are used, the cost and weight of the cellular phone is increased. In any case, the prior art grounding of the metallic layers with the inner sides of the casings 12, 14 is unsatisfactory because the metallic layers are electrically connected to the ground layer of the circuit board 20 by a limited numbers of screws. The question of how to reduce the quantity of metallic shields while improving the grounding of the metallic layer on the inner side of the casing and maintaining optimal performance of each of the functional units of the cellular phone is very important for cellular phone design.
It is therefore a primary objective of the present invention to provide a cellular phone with an insulating envelope for preventing leakage of electromagnetic radiation to solve the above mentioned problem.
In a preferred embodiment, the present invention provides a cellular phone comprising:
a housing having front and rear casings wherein the rear casing comprises a metallic layer coated on an inner side of the rear casing for insulating electromagnetic radiation;
a circuit board installed in the housing having a board surface and an antenna connector installed at an upper end of the board surface;
an antenna installed at an upper end of the housing and electrically connected with the antenna connector at the upper end of the board surface for receiving or emitting electromagnetic radiation; and
an elastic conductor;
wherein when the front and rear casings are connected, the elastic conductor can be elastically clamped between the board surface of the circuit board and the metallic layer on the inner side of the rear casing so that the metallic layer on the inner side of the rear casing, the upper end of the board surface and the elastic conductor will form an insulating envelope for preventing the electromagnetic radiation emitted from the antenna connector from interfering with other circuits of the cellular phone which are positioned inside the housing of the cellular phone and outside the insulating envelope.
It is an advantage of the present invention that not only is the quantity of metallic shields on the circuit board reduced but also radiation interference between the functional units is reduced.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.